Quantum conversion

The reduction of NADP+ was studied as a function of exciting light wavelength both in the presence and absence of the poison DCMU (which blocks the flow of electrons through Pigment System 2), (Hoch and Martin, 1963). When DCMU was present 

The photochemical transfer of a single electron should result in the formation of species with unpaired electrons. These species can be expected to give EPR signals, and it has been of interest to see if the EPR signals produced by the absorption of light in photosynthetic material can be correlated with the P700 reaction. 

Beinert and Kok (1963) compared the number of unpaired electrons (as indicated by EPR signals) produced in illuminated photosynthetic material of various types with the amount of P700. 

Clayton (1962) and Loach et al. (1963) demonstrated a relationship between optical changes in absorption spectra and EPR signals with photosynthetic bacteria. In those experiments, light-induced absorption changes and EPR signals could be simulated in the dark by chemical oxidation. 

Calvin (1958) has proposed essentially the following mechanism for the primary quantum conversion steps of photosynthesis. Following the absorption of light by any of the antennae chlorophyll molecules in the quantasome or chromatophore, the excited 

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Chloropentammine Ir (HI) complex, incomplete Ir (III) autoreduction, 39 151-152 Chloroplasts, quantum conversion in, 14 1 1 -Chloroprop-2-ene thermal decomposition, 41 80 Chlorpromazine, reactivity with EDA complexes, 20 333, 336 CH O, 32 374-375 CH3OH, oxidation, 38 21-23 Cholestenone, hydrogenation, 25 57, 58 Cholesterol, biosynthesis of, 25 382 Cholinesterases, stracture of active surface, 10 130... 

Quantum-chemical cluster models, 34 131-202 computer programs, 34 134 methods, 34 135-138 for chemisorption, 34 135 the local approach, 34 132 molecular orbital methods, 34 135 for surface structures, 34 135 valence bond method, 34 135 Quantum chemistry, heat of chemisorption determination, 37 151-154 Quantum conversion, in chloroplasts, 14 1 Quantum mechanical simulations bond activation, 42 2, 84—107 Quasi-elastic neutron scattering benzene... 

However, a major difficulty associated with this approach is the restriction of overall quantum conversion efficiencies due to low light absorption by thin dye layers. Thick dye layers, although they may absorb all of the light, do not result in significantly greater conversion efficiencies, since they suffer from increased quenching probabilities and large resistances. 

Calvin M. Photosynthesis and quantum conversion. In Pullman K, ed. Horizons in Biochemistry. New York Academic Press, 1962. 

What we are concerned with is not what happens after this primary quantum conversion act but only what the nature of the primary act (or acts) itself may be. There is a good deal of information developing in the region of the reaction following the primary process, particularly on the reducing side, and relatively little on the oxidized side yet, and some on the recombination. But it is the primary act itself that we will be concerned with here. 

In order to see what our train of thought was over the course of the years, one should remember the structure of chlorophyll and a few things that have been done in an attempt to try and find out what the primary quantum conversion act of photosynthesis was. There are a number of peculiarities about the structure of chlorophyll which have led many chemists to suggest a number of reactions which might possibly be involved in the primary quantum conversion act. 

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